The present invention relates to a pump system, and to a lubrication and hydraulic control system including such pumps.
Oil within a single machine may be used for many purposes. In the context of a constant speed generator for use within an aircraft electrical power generation system, the oil may be used to lubricate bearings and other rotating parts, to act as a coolant within the generator, and may also act as a control fluid within a speed conversion system, such as a continuously variable transmission, used to ensure that a variable input speed from a prime mover is converted to a near constant generator speed. Use of oil as a coolant generally requires a high volume low pressure supply of oil. However, use of oil as a control fluid generally requires a high pressure supply of oil.
There is a penalty to be paid, in terms of energy consumed by the pumps and heat dumped into the oil, in pumping oil to high pressure. For this reason it is not desirable to use a single pump to supply oil at high pressure and high volume with the intention of tapping some of this oil off to a lower pressure for use as a coolant. Furthermore, high pressure pumps inevitably work under more stress than low pressure pumps and tend to require more frequent servicing and/or have shorter service lives.
According to a first aspect of the present invention, there is provided a pump system comprising a first pump for providing a first flow of liquid for use within a cooling or lubrication system, and a second pump for providing a second flow of liquid, wherein the pumps are drivingly connected via respective coupling elements to an input element, and arranged such that failure of the second pump resulting in it requiring an increased torque at an input to the pump causes the second pump to be drivingly disconnected from the input element.
Preferably the second pump is arranged to supply liquid for use in a control system. The second pump may, for example, be arranged to supply oil for use in hydraulic actuators associated with a continuously variable transmission system. Such a system, may for example, comprise a drive belt running between two continuously variable ratio pulleys. Preferably the first and second pumps are coaxially mounted. The drive for the second pump may be provided via the first pump.
In a preferred arrangement, the first pump is driven via a first pump drive shaft and the second pump is driven via a second pump drive shaft which is coaxial with the first pump drive shaft. The first pump drive shaft and the second pump drive shaft advantageously have drive regions which receive a driving torque to be transmitted via the drive shafts and pump regions which engage with the pumps or suitable intermediate elements such that torque can be transferred from the shafts to the pumps. Each shaft also has a shear region, for example in the form of a shear neck, located between the drive region and the pump region thereof such that in the event of excessive torque being transmitted through either shaft, that shaft can shear, so as to provide protection against mechanical failure in the associated pump, while the remaining shaft continues to transmit drive to its associated pump.
Advantageously the first and second pump drive shafts are attached to a shared drive region.
Preferably the second pump is in splined engagement, via a coupling, with a drive shaft supplying motive power to it.
Preferably the second pump is attached to a mounting point such that the fixing points for the second pump do not require disassembly or substantial disassembly of the housing containing the machine serviced by the pump. Advantageously the fixing points are on an external wall of the housing. Thus the high pressure pump may be implemented as a unit removable and replaceable from the exterior of the housing. The use of the splined coupling means that disconnection of the pump from its drive and reconnection to the drive can be achieved merely by an axial movement of the second pump.
It is thus possible to provide a pump system for a continuously variable transmission and generator within a housing, wherein a low pressure pump is provided for supplying oil for lubrication and cooling components within the continuously variable transmission and generator and a high pressure pump is provided for supplying high pressure oil to control actuators of the continuously variable transmission, and wherein failure or damage of the high pressure pump causes it to become drivingly disconnected thereby leaving the low pressure pump continuing to operate in order that it can maintain a supply of coolant to components within the housing. In this event, the continuously variable transmission defaults to minimum generator drive speed.
It is further possible to provide a pump mounted to a fixing on the external surface of the housing containing the pump, with said pump being connected to a drive element via a coupling which allows the pump to be disconnected from the element by an axial movement in the first direction and connected to the drive element by an axial movement in a second direction opposed to the first direction, and wherein the coupling has a disconnect region therein designed to drivingly disconnect the pump when the torque acting on the coupling exceeds a predetermined value. Alternatively the pump may be mounted in a recess accessible either directly from the external surface of the housing or easily accessible via the removal on an element such as a plate.